How many electrons are there in the average bowl of cereal?

Well typically breakfast consists of around 200 grams of cereal and roughly 200 millilitres of milk. For these purposes I will make some assumptions:

First assume that the cereal is made up completely of carbon. 12 grams of carbon contains approximately 6.023 x 1023 atoms of carbon (The Avogadro Number from earlier on). So 200 grams of carbon contains (200/12) ~ 17 x 6.023 x 1023 atoms. Each atom of carbon contains 6 electrons. So the final total is 6 x 17 x 6.023 x 1023 which comes to 6.14 x 1025 atoms.

Next assume that the milk is made up completely of water. 18 grams of water contains approximately 6.023 x 1023 molecules of water (The Avogadro Number again). So 200 grams of water contains (200/18) ~ 11 x 6.023 x 1023 atoms. Each molecule of water contains 2 atoms of hydrogen each with 1 electron and 1 atom of oxygen each with 8 electrons which makes 10 electrons per molecule. . So the final total is 10 x 11 x 6.023 x 1023 which comes to 6.63 x 1025

These two numbers are so similar that it barely makes any difference what we assume – so 400 g of cereal – made up of any mix of milk/cereal contains roughly 6.14 x 1025 + 6.63 x 1025 ~ 1.27 x 1026 electrons.